I agree since the IW had the infinity stones. Without them in a straight up fight I would still edge the Watch but by no means a certainty. The Authority have the power to battle and win against some vastly powered foes though they also were brought low by Kev and other less powerful opponents. If the authority knows who they are facing and a little prep they could take out the watch. However the reverse is also true. I am thinking in terms of the Authority circa 1995-2005.